What prevents a self-amplifying reaction and nuclear explosion in power plants?

Control rods that absorb extra neutrons are crucial in preventing a self-amplifying reaction and potential nuclear explosion in power plants. In a nuclear reactor, a fission reaction occurs when uranium or plutonium nuclei split, releasing a significant amount of energy and additional neutrons. If too many neutrons are present, they can cause further fission reactions, leading to an uncontrolled chain reaction.

Control rods are made from materials that are effective at capturing neutrons, such as boron, cadmium, or hafnium. By inserting these rods into the reactor core, operators can regulate the number of free neutrons and maintain the fission reaction at a steady and safe level. This modulation ensures that the reaction remains critical (balancing between a self-sustaining reaction and extinction) rather than becoming supercritical, which would lead to an explosive release of energy.

Thus, the critical role played by control rods is fundamental in ensuring nuclear reactors operate safely and efficiently, keeping the reactor stable and preventing any risk of an explosive scenario.